Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $152.94   8.226%   $165.5208   $165.52   $165.50   $165.50  
  Purchase #2 $169.47   13.617%   $192.5467   $192.55   $192.55   $192.50  
  Purchase #3 $50.98   13.547%   $57.8863   $57.89   $57.90   $57.90  
  Purchase #4 $66.93   4.685%   $70.0657   $70.07   $70.05   $70.10  
  Purchase #5 $203.56   10.575%   $225.0865   $225.09   $225.10   $225.10  
  Purchase #6 $209.76   4.454%   $219.1027   $219.10   $219.10   $219.10  
  Purchase #7 $74.30   8.795%   $80.8347   $80.83   $80.85   $80.80  
  7 purchase totals = $927.94       $1,011.0434   $1,011.05   $1,011.05   $1,011.00